离子液体电沉积法制备锗基锂电池负极材料

发布时间：2018-03-04 11:10

本文选题：锂离子电池　切入点：负极　出处：《中国科学院大学(中国科学院过程工程研究所)》2017年硕士论文　论文类型：学位论文

【摘要】：当前已经商业化的锂电池负极材料,主流产品为人造石墨和改性天然石墨,还有少量产业化应用的钛酸锂,可以基本满足一般电子产品、储能电池的要求。但由于它们的理论容量均不高,不能满足对电池储能具有更高要求的电动汽车等领域的发展需求。因此需要开发更多的具有高容量的电极材料,来提升电池能量密度。本课题选取锗作为研究对象,它的理论储锂容量高达1600mAhg-1,远远高于石墨(372 mAhg-1),非常有潜力提高锂电池的性能。然而,锗负极材料在应用到锂电池中时,也面临着较大的问题与挑战,即在充放电过程中,随着Li+在电极材料中的嵌入与脱出,电极材料会发生不可逆的体积变化,并且膨胀率高达370%。这会直接引起材料的内部相互挤压,导致材料破碎并从集流体脱离下来,使锂电池的循环稳定性大幅度降低。本课题通过电沉积的方法,从离子液体中直接将锗离子还原,沉积到具有特殊结构的集流体上,得到Ge镀层/特殊结构集流体的复合电极。电化学测试表明,这种方法制备的负极可以较大程度地改善锗的电化学性能,主要工作包括:(1)以铜网集流体作为沉积基底,通过离子液体电沉积的方法,实现了在其表面上电沉积上一层致密的锗层。以此锗/铜网复合物直接作为锂电池的负极,研究材料结构对电池电化学性能的影响。经沉积的锗层由致密的纳米颗粒组成,且与铜网之间的结合比较牢固,不易脱离。研究表明,从第2次起到第55次循环,容量衰退减缓,比容量由原来的873 mAh g-1下降到了 672 mAh g-1,容量保持率为76.9%。(2)以碳布集流体作为沉积基底,同样以离子液体电沉积的方法,制备锗/碳布复合电极。扫描电镜表征发现,在碳布纤维表面沉积的锗层具有"内疏外密"的双层结构。这种双层结构的锗镀层材料,不仅具有较高的比容量,还有效地缓解了材料在充放电过程中的体积变化严重的问题,使得材料的结构稳定性得以完善。电化学测试表明,在循环100次以后,电池的容量仍然高达989 mAh g-1,具有较高的容量保持率。
[Abstract]:At present, the commercial cathode materials for lithium batteries are made of artificial graphite and modified natural graphite, and a small amount of lithium titanate, which is used industrially, can basically meet the needs of general electronic products. However, the theoretical capacity of these batteries is not high enough to meet the development needs of electric vehicles with higher requirements for battery energy storage. Therefore, it is necessary to develop more electrode materials with high capacity. In this paper, germanium is selected as the research object. Its theoretical lithium storage capacity is as high as 1600mAhg-1, which is much higher than that of graphite (372mAhg-1g), which has great potential to improve the performance of lithium-ion batteries. However, germanium anode materials are used in lithium-ion batteries. In the process of charge and discharge, the electrode material will change irreversibly with the intercalation and release of Li in the electrode material. And the expansion rate is as high as 370. This will directly cause the internal extrusion of the material, which will cause the material to break up and separate from the collecting fluid, so that the cycle stability of the lithium battery will be greatly reduced. GE coating / special structure composite electrode was obtained by directly reducing germanium ion from ionic liquid and depositing GE ion onto the collector with special structure. The anode prepared by this method can greatly improve the electrochemical performance of germanium. A dense layer of germanium on the surface was realized. The GE / Cu net composite was used directly as the negative electrode of the lithium battery. The effect of material structure on the electrochemical performance of the battery was studied. The deposited germanium layer was composed of dense nanocrystalline particles. And the bond with the copper mesh is strong and difficult to detach. Research shows that from the second to the 55th cycle, the capacity decline slows down. The specific capacity decreased from 873 mAh g ~ (-1) to 672 mAh g ~ (-1), and the capacity retention was 76.9%. The germanium layer deposited on the surface of carbon cloth fiber has a double-layer structure of "internal and external density". This kind of bilayer structure germanium coating material not only has a high specific capacity, but also effectively alleviates the serious problem of volume change in the process of charge and discharge. The electrochemical measurements show that the capacity of the battery is as high as 989 mAh g-1 after 100th cycle, and has a high capacity retention rate.
【学位授予单位】：中国科学院大学(中国科学院过程工程研究所)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM912

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